Activation of silver catalysts



- latente'd Mar. 26, 1940 I v p 2,194,602

UNITED STATES PATENT OFFICE ACTIVATION F SILVER CATALYSTS George H. Law, South Charleston, and Henry C. Chitwood, Charleston, W. Va., auignors to Carbide and Carbon Chemicals Corporation, a corporation of New York No Drawing. Application December 29. 1938, Serial No. 248,209

13 Claims. (Cl. 260-348) This invention provides improvements in the either the silver catalysts as disclosed by Lefort process of making oleilne oxides by the direct or the improved catalysts disclosed in the cocatalytlc oxidation of oleflnes by means of mopending application of McNamee and Blair, 1

lecular oxygen. Specifically, it provides amethod higher yields of olefine oxide are obtained by 5 for activating catalysts which are initially low in r tarding the complete oxidation of the oleflne activity or which have lost activity through use. through the addition to the reactants of very The process of oxidizing olefines directly to small amounts (less than 0.1% by volume) of oleflne oxides by means of molecular oxygen in certain deactivating (or anti-catalytic) materials, the presence of surface catalysts has been deor repressants such as ethylene dichloride, xylene,

o scribed in Reissue Patent 20,370 to T. E. Lefort, sulfur trioxide and certain other compounds. dated May 18, 1937. In that patent the use 01 This improvement is described in our copending such surface catalysts as those formed essentially application Serial No. 157,884, filed August 7, of silver is disclosed. Silver alone, or activated 1937. However, the addition of such materials by the-addition of small amounts of gold, copper does not prolong the activity of the catalyst, and

or iron, is a very desirable catalyst for the oxidaa time may be eventually reached when the cata- 15 tion of olefins directly to form oleflne oxides. lyst must be eac vated n orde to per t con- Like many other catalytic surfaces, these silvertinued operation of the process in the most ecocontaining catalysts are difilcult to prepare in an nomical fashion. initially highly active form, and when so pre- The principal object of this invention is to prepared they suffer a gradual loss in activity as the vide a convenient, simple and effective method of length ofservlce increases. Ordinarily, catalytic activating silver surface catalysts for use in the surfaces may be rendered active initially, or after direct oxidation of olefines to olefine oxides. The use, by alternative oxidation and reduction, in activation of the catalyst, as disclosed herein, does which the oxidation is accomplished by passing ot require equipment constructed of especially air or oxygen over the heated metal and the reresistant material, such as stainless steel and the duction of the metal oxide is obtained through like, but may be conducted with complete success contact with hydrogen or other reducing gas. in the presence of iron or other conventional ma- Due to the low dissociation temperature of silver terials of construction. The invention also inoxide (at atmospheric pressure) it is not possible eludes the improvements in the process of oxidizto oxidize silver easily by air or oxygen. For this log oleflnes directly to form olefine oxides which 30 reason, special conditions are required for the are achieved by h u e f the new method of preparation of silver surface catalysts in those activation, all as hereinafter described. highly active forms desired for the most econom- The activation of silver surface catalysts may ical operation of the Lefort process. be accomplished by bringing the catalyst in con- In. a copending application of G. H. Law, Serial tact with an aqueous solution of barium, stron- No. 157,883, filed August 7, 1937, a process is detium or'lithium hydroxide, or a mixture of these, scribed whereby silver surface catalysts suitable provided, w r, t the t yst h s firs been for use in the Lefort process may be activated by treated with a repressant (or anticatalyst) such treating the silver surface with ozone and water as ethylene dichloride, chlorine, sulfur chloride, vapor at relatively low temperatures. followed by Sulfur tl'ioxide. nitrogen dioxide. 1 Other h lO- 0 reduction of the silver peroxide formed with hygen-containing or acid-forming material. drogen at higher temperatures. In this process, Surface catalysts which contain silver in any reduction of the silver peroxide can be replaced physical form can be treated by the process of by a treatment with a solution of barium, stronthis invention to effect pronounced increase in,

tium or lithium hydroxide. This latter treatment or to restore their original, activity in the Lefort 5 produces a catalytic material which is of the same reaction. (The extent to which the activity is ingeneral type as that formed of a mixture of silver creased is dependent upon the original form of (or silver oxide) and peroxides of the alkali or the silver and the number of times the activation alkaline earth metals. Catalysts of thislatter process is repeated. In general, finely divided type are exceptionally active and desirable for silver (or silver oxide) having a roughened suruse in the Lefort process, and they form the subace is the pr f rr d f rm f th c ly t It is ject matter of a copending application of R. W. desirable, but not essential, to use a granular McNamee and C. M. Blair, Serial No. 157,854, inert material, such as porous artificial silica filed August 7, 1937. stone, granular ceramically bonded alumina,

In the operation of the Lefort process, using sandstone and the like, as a support for the u flnely divided silver. The silver may be deposited on such a support by chemical means, or mechanically from suspensions of finely divided metallic silver or silver oxide. The amount of silver in 5 those catalysts which employ supporting materials may vary over a wide range, but, in general, from about 4% to about 20% by weight is satisfactory.

Although the catalyst may be treated with the 10 repressant or deactivator at any time prior to contact with the barium, strontium or lithium hydroxide solution, the treatment may most advantageously be conducted simultaneously with the oxidation reaction of the olefines, inasmuch 5 as the presence of very small amounts of repressant (less than 0.1%) increases the efilcienoy of conversion of the oleflnes to olefine oxides by limiting the formation of carbon dioxide and permitting better heat control of the process, as disclosed in our copending application Serial No. 157,884, mentioned above. However, if just before reactivation the catalyst is further deactivated by treatment with a larger amount of repressant, the resulting acac tivity after treatment with the hydroxide is greater than that attained by employing the hydroxide treatment on the catalyst in a more active condition.

In the following examples, which will serve to :0 illustrate further the nature of the invention, the reaction tubes were one inch iron pipes three feet in length. Each tube was jacketed and wound forelectrical heating, and the temperature was regulated by boiling an organic liquid in the 35 jacket. The catalyst sample was placed in the lower part of the tube, and the upper part, or preheating section, was packed with a porous artificial silica stone. A gas mixture containing 10% ethylene and 90% air was passed over the cata- 40 lyst at a rate of 50 liters per hour. Temperatures were measured within a thermocouple well imbedded in the catalyst 01 within the boiling liquid in the jacket. Overall yields and efliciencies were calculated from analysis of the exit gases for 45 ethylene oxide, carbon dioxide and unreacted ethylene. By overall yield we mean the ratio of ethylene oxide produced to that theoretically obtainable from the amount of ethylene introduced into the reaction, and by efiiciencywe mean the 50 ratio of ethylene oxide produced to that theoretically obtainable from the amount of ethylene which has undergone a chemical reaction in the process. Small amounts (less than 0.1% of the total volume) of the repressant were admitted as needed to facilitate control of the reaction. Approximately constant conditions of operation were maintained, and measurements were made at the same temperature before and after deactivation, and after reactivation. The proportions of the materials are parts by weight.

Example I 65 The catalyst was prepared by heating and stir- The overall yield gradually decreased with time. and barium hydroxide solution (25% by weight as the octalrvdrate) was used periodically to restore the activity by allowing it to stand on the catalyst for five minutes at 90 C. In the follow- 5 ing table are summarized the data obtained over a total of 1945 hours of operation with three reactivations.

' Overall Efli- 10 Elapsed time of operation, hours yield, clency, percent percent REAOTIVATED WITH 25% BARIUM HYDROXIDE REAOTIVA'IED WITH BARIUM HYDROXIDE Example II The catalyst was a sample prepared from 90 parts of silver oxide, 9 parts barium dioxide and 30 260 parts of granular ceramically bonded alumina crushed and graded between 2 and 4 mesh screens. This catalyst had previously been deactivated and used under a number of conditions, so that its activity before the test was abnormally low. The apparatus and method of operation were the same as in Example 1, except that an uncored reaction tube was used and the temperatures were measured in the jacket.

The catalyst was intentionally deactivated by introducing an excess amount of ethylene dichloride into the feed gases. The ethylene dichloride (or repressant) is in the feed gases in excess when its presence retards the oxidation of the olefine to olefine oxide more than it retards the oxidation of the oleflne to carbon dioxide and water. After running for several hours to test its activity, the catalyst was cooled to 100 C., thoroughly leached with hot water and soaked in a solution of barium hydroxide (octahydrate) at 100 C. for five minutes. After draining, operation was resumed. The following measurements of overall yield and eiilciency were made at 280 to 285 C.

Overall percent Before deactivation Three hours after deactivation After reactivation Example III An unpromoted catalyst prepared from 16.5 parts of silver oxide on 300 parts of a 2 to 4 mesh sandstone was used in an uncored tube in the same manner as described under Example II. It was tested and found to possess a moderate initial activity. Ethylene dichloride was admitted in excess and the activity declined until no qualitative test for ethylene oxide in the exit gas could be obtained at 250 C. The catalyst was then treated with 25% barium hydroxide solution for five minutes at 100 C. On resuming operation a 30.5% overall yield of ethylene oxide was obtained at 250 C. with 50% efficiency. Example IV A catalyst prepared from parts of silver oxide and 4.5 parts of strontium hydroxide octahydrate promoter, deposited on 260 parts of 2 to 4 mesh granular ceramically bonded alumina was used in an uncored tube. After testing for initial Overall Ei'iiciyield, ency, percent percent Before deactivation 24. 5 72 After deactivation with ethylene dichloride m 3. 2 50 After soaking with 10% strontium hydroxide for 10 minutes at 90 C 4. 2 56 After soaking with 20% strontium hydroxide for 15 minutes at C 2 53 1, Example V A catalyst prepared from 15 parts of silver oxide and 1.5 parts of barium dioxide promoter, deposited on 180 parts of 4 to 8 meshporous silica stone was used in a cored tube. After testing for initial activity it was deactivated by feeding an excess of sulfur chloride. Reactivation was then conducted by periodic treatment with 25% aqueous barium hydroxide octahydrate. The following measurements of overall yield and efliciency were madeat 295 to 299 C.

Overall Efficiyield, ency, percent percent Before deactivation 39. 0 61. 0 After deactivation 7. 7 53. 5

43 hours after reactivation W1 25% barium hydroxide at 90 C 23. 5 61. 7 After a second reactivation with 25% barium hydroxide at 90 C 33. 0 55. 5

Example VI The catalyst, prepared from 7.5 parts of silver oxide, 0.75 part of barium dioxide and 300 parts of 2 to 4 mesh sandstone, was used in an uncored tube. The apparatus and method of operation were the same as in Example II.

The catalyst was intentionally deactivated by introducing an excess amount of sulfur trioxide into the feed gases. After running for several hours to test its activity, the catalyst was cooled to about 90 (Land soaked for ten minutes in 20% aqueous barium hydroxide octahydrate solution. After draining, operation was resumed. The following measurements of overall yield and efliciency were made at 263 to 264 0.

About 90% of the original activity of a deactivated catalyst of relatively low silver content can be restored by this method. Catalysts of high silver content which are originally very active at low temperatures are not as completely revivifled, somewhat hig required after reactivatio yield and efficiency.

It has been found that successive treatments with barium, strontium or lithium hydroxide becomeless and less effective, probably due to an accumulation of too much of this material on the catalyst. If, after a number of reactivations, the catalyst is leached with hot water, a greater activity results after the next reactivation.

Other compounds may be used as the repressant, or deactivator, than ethylene dichloride. In general, any compounds which are gaseous in small concentrations between C. and 400 0., and will react with the silver surface of the catalyst to form silver compounds which are converted to silver oxide or hydroxide by the er temperatures being to attain the original action of barium, strontium or lithium hydroxide,

are suitable as the deactivators in this process. For example, acid-forming compounds such as nitrogen dioxide, chlorine, sulfur trioxide, and the like may be used. However, the halogenbearing organic compounds are more desirable, and the chlorinated ones are preferred.

Variations in the specific procedures shown in the foregoing examples will be apparent and may be adopted without departing from the essentials of this invention. The catalysts activated in accordance with this invention can be used to cause olefines, especially ethylene, to combine directly with molecular oxygen to form the corresponding olefine oxide at temperatures between about 150 and 400 C. Also, as shown by Lefort, the reaction proceeds either at atmospheric pressure or at increased or decreased pressums, and any desired proportion of the olefine and oxygen or air (or other oxygen-containing gas) can be used.

Other modifications of the process will be apparent and are included within the invention as defined by the appended claims.

This application is a continuation-in-part of copending application Serial No. 171,892, filed October 30, 1937.

We claim:

1. Process for activating silver surface catalysts for use in effecting the direct chemical combination of olefines with molecular oxygen to form olefine oxides, which comprises bringing the catalyst in contact with a compound, small concentrations of which are gaseous between 150 C. and 400 C., and which will react with the silver surface of the catalyst to form silver compounds which are converted to silver oxide or hydroxide by the action of barium, strontium or lithium hydroxide, and thereafter treating the catalyst with a member of the group consisting of barium, strontium and lithium hydroxides.

2. Process for activating silver surface catalysts for use in effecting the direct chemical combination of olefines with molecular oxygen to form olefine oxides, which comprises treating the catalyst with a repressant in the gaseous phase, said repressant being chosen from the group consisting of halogenated organic compounds and acid forming compounds, and thereafter treating the catalyst with an aqueous solution of a compound selected from the group consisting of barium, strontium and lithium hydroxides to form an active surface catalyst. 3. Process for activating silver surface catalysts for use in effecting the direct chemical combination of olefines with molecular oxygen to form olenne oxides, which comprises treating the catalyst with a repressant in the gaseous phase, said repressant being a halogenated organic compound, and thereafter treating the catalyst with an aqueous solution of a compound selected from the group consisting of barium, strontium and lithium hydroxides to form an active surface catalyst.

4. Process for activating silver surface catalysts for use in effecting thedirect chemical combination of oleflnes with molecular oxygen to form olefine oxides, which comprises treating the catalyst with a chlorinated organic compound in the gaseous phase at a temperature between 150 and 400 C. and subjecting the thus treated catalyst to the action of an aqueous solution of a compound selected from the group consisting of barium, strontium and lithium hydroxides to form an active surface catalyst.

5. Process for activating silver surface catalysts for use in effecting the direct chemical combination of olefines with molecular oxygen to'form olefine oxides, which comprises treating the catalyst with ethylene dichloride and subjecting the thus treated catalyst to the action of an aqueous solution of a compound selected from the group consisting of barium, strontium and lithium hydroxides to form an active surface catalyst.

6. Process for activating silver surface catalysts for use in effecting the direct chemical combination of olefines with molecular oxygen to form olefine oxides, which comprises treating the catalyst with a halogenated organic compound in the gaseous phase at a temperature between 150 and 400 Grand subjecting the thus treated catalyst to the action of an aqueous solution of barium hydroxide to form an active surface catalyst.

'7. Process for activating silver surface catalysts for use in effecting the direct chemical combination of oleflnes with molecular oxygen to form oleflne oxides, which comprises treating the catalyst with a chlorinated organic compound in the gaseous phase at a temperature between 150 and 400 C. and subjecting the thus treated catalyst to the action of an aqueous solution of barium hydroxide to form an active surface catalyst.

8. Process for activating silver surface catalysts for use in effecting the direct chemical combination of olefines with molecular oxygen to form olefine oxides, which comprises treating the catalyst with ethylene dichloride at a tempera ture between 150 and 400 C. and subjecting the thus treated catalyst to the action of an aqueous solution of barium hydroxide to form an active surface catalyst.

9. Process for activating silver surface catalysts for use in effecting the direct chemical combination of oleflnes with molecular oxygen to form olefine oxides, which comprises treating the catalyst with a halogenated organic compound in the gaseous phase at a temperature between 150 and 400 C. and subjecting the thus treated catalyst to the action of an aqueous solution of strontium hydroxide to form an active surface catalyst.

10. Process for activating silver surface'catalysts for use in effecting the direct chemical combination of oiefines with molecular oxygen to form oleflne oxides, which comprises treating the catalyst with ethylene dichloride at a temperature between 150 and 400 C. and subjecting the thus treated catalyst to the action of an aqueous solution of strontium hydroxide to form an active surface catalyst.

11. Process for activating silver surface catalysts for use in effecting the direct chemical combination of olefines with molecular oxygen to form oleflne oxides, which comprises treating the catalyst with a halogenated organic compound in the gaseous phase at a temperature between 150 and 400 C. and subjecting the thus treated catalyst to the action of an aqueous solution of lithium hydroxide to form an active surface catalyst.

12. Process of making ethylene oxide by the direct chemical combination of ethylene with molecular oxygen at temperatures between about 150 and 400 C. in the presence of a surface catalyst, which comprises employing a silver surface catalyst activated by treating the catalytic surface with a chlorinated organic compound in the gaseous phase and thereafter treating the catalyst with a compound selected from the group. consisting of barium, strontium and lithium hydroxides to produce an active catalytic surface.

13. Process of making ethylene oxide by the direct chemical combination of ethylene with molecular oxygen at temperatures between about 150 and 400 C. in the presence of a surface catalyst, which comprises employing a silver surface catalyst activated by treating the catalytic surface with ethylene dichloride in the gaseous phase and thereafter treating the catalyst with a compound selected from the group consisting of barium, strontium and lithium hydroxides to produce an active catalytic surface.

GEORGE H. LAW. HENRY C. CHITWOOD. 

